Everything Everywhere, the mobile operator created by the merger of T-Mobile and Orange, is to cut 550 jobs as its new boss takes a further axe to costs.

Job losses equivalent to 4% of the workforce will be concentrated on support roles, mainly in Bristol, London and Hatfield in Hertfordshire. The company said it was trying to protect staff employed in call centres and its retail outlets, with cuts also falling on temporary agency staff.

An Everything Everywhere spokesman said: "Following a review of its business, Everything Everywhere has announced proposed organisational changes to support the company as it transitions from integrating two businesses to a new phase focussed on accelerating the delivery of the company ambitions."

The merger between T-Mobile and Orange, which created the largest mobile group in the UK and which operates the mobile phones of 28 million Britons, has already seen 1,200 staff depart in an earlier bout of cost-cutting as the newly created business targeted duplication in its workforce. Everything Everywhere is committed to a multi-billion pound cost-saving programme, with joint owners France Télécom and Deutsche Telekom basing much of the logic of a merger on a commitment to slash £3.5bn from the combined businesses by 2014.

There have been suggestions that, because no T-Mobile executives survived Swantee's September cull, it has not been a merger of equals. The company has also deployed innovative internal PR methods to inform staff of their fate. Some were warned of their looming redundancy by a colour-coded "traffic light" system. Middle managers and back office staff whose jobs were "at risk" were shown a red light at workforce gatherings while some colleagues saw a yellow light, meaning they had to reapply for their posts.

CWU deputy general secretary Andy Kerr said: "This is disappointing news and will be very difficult for staff facing redundancy. We predicted large job losses when the merger was announced and redundancies in support roles will not come as a great shock to most, but that doesn't make it any easier for those affected. Staff are having to pay a massive price for the year-old merger of Orange and T Mobile.

"The recent culling of senior executives following the departure of Tom Alexander and appointment of Olaf Swantee was the inevitable trigger for the cutbacks being visited on ordinary workers in the company. In talks with the company we are at least reassured there are no plans to cut frontline staff in call centres and shops, or to close buildings. We are offering as much practical support to our members in the back office support functions as possible during this difficult time."